Oilwell tubing connection

Abstract

A connection (20) for oilwell tubing and the like is disclosed which has the same outer diameter (21) as does the tubing joints (8 and 9) that it connects. Tubing joints are formed internally with a tapered thread (6 and 7) having a loadbearing flank angle (75° or more) that negates pullout tendency. A mating coupling (2) having external threads (3 and 4) may be provided with a bore 10 so as to clear a driftbar. Coupling (2) may be provided with bore (13) extending from (14 to 15) so as to develop substantially, a 100% joint strength.

I claim: 
     
       1. The combination of a connection for joints of oilwell tubing or the like, comprising: a tubular coupling formed with tapered external threads thereon at each end for sealing engagement with tapered internal threads formed within the ends of the tubing joints to be connected, the connection being dimensioned and made of suitable material such that at full make-up, circumferential stresses within the small end of the external thread and within the large end of the internal thread are substantially at the same percentages of the yield stresses of the respective materials from which the joints and couplings are formed. 
     
     
       2. A high efficiency connection for joints of oilwell tubing or the like, comprising: a joint of pipe having no increase in wall thickness near the ends thereof, formed at each end with tapered internal threads; a tubular coupling formed at each end with tapered external threads for sealing engagement with said internal threads so as to connect two joints of pipe together, the threads being of sufficient length and taper such that the pipe wall strength in the area of the smallest diameter of thread engagement being at least; three-fourths of the nominal pipe wall strength. 
     
     
       3. The invention of claim 2 further comprising: the coupling being formed with a shoulder so as to abut the end of the pipe joint upon full make-up of the connection. 
     
     
       4. The invention of claim 3, further comprising: the threads and shoulders being dimensioned such that circumferential compressive stresses at the small end of the male thread are substantially near the unit yield strength of the material from which the coupling is formed. 
     
     
       5. The invention of claim 1 wherein the inner diameter of the coupling is greater than the drift diameter of the pipe. 
     
     
       6. The invention of claim 2 further comprising: a neck at the base of the external thread being formed with a cross-section wall area less than the nominal cross-section wall area of the pipe; the coupling being formed of a material sufficiently stronger than the pipe material such that the external thread of the coupling can contract further than it could were it made of the pipe material, so as to effectively seal a higher fluid pressure. 
     
     
       7. The invention of claim 1 further comprising: the coupling being formed with a bore of smaller dimension than the pipe bore. 
     
     
       8. The invention of the claim 2 further comprising: the coupling being formed of a material having greater strength than the pipe material such that the combined wall strength through the connection effects a greater collapse resistance than does the pipe wall. 
     
     
       9. The invention of claim 8 wherein the collapse resistance of the connection is sufficiently greater than the collapse resistance of the pipe wall such that neck-down and failure of the unthreaded pipe wall will occur before failure of the connection will occur upon the application of increasing tension loads to an assembled connection. 
     
     
       10. The invention of claim 9 further comprising: the pipe wall area at the last engaged thread being less than the nominal pipe wall area, neck-down and failure not occurring at the last engaged thread because of said greater collapse resistance. 
     
     
       11. The invention of claim 1 further comprising: the external thread being formed on a taper of smaller included angle that is the taper of the internal thread such that at full make-up of the connection, a first predetermined circumferential stress is effected in the coupling at the smallest diameter of the external thread and a second predetermined circumferential stress of less magnitude than the first stress is effected in the pipe wall at the largest diameter of thread engagement. 
     
     
       12. The invention of claim 11 wherein make-up of the connection comprises: first contact between the external thread and the internal thread at the smallest diameter of the external thread; at full make-up of the connection, full engagement of the external threads is effected. 
     
     
       13. The invention of claim 1 wherein the threads are formed with load flanks and stab flanks, comprising: the load flanks being formed at an angle of 75% or greater with respect to the tubular axis; the stab flank being formed at an angle of lesser degree with respect to the tubular axis; the load flanks and the stab flanks being connected at the roots and crests by cooperating radii such that upon full make-up of the connection, increased sealing engagement is effected along the full thread engagement length. 
     
     
       14. The invention of claim 2 wherein the internal threads extend substantially to the pipe bore. 
     
     
       15. The invention of claim 1 wherein: the strength of the pipe wall at the thread root adjacent the last engaged thread toward the smaller diameter end of the taper is greater than 75% of the pipe wall strength at mid-section of the pipe so as to provide a high strength connection for non-upset pipe. 
     
     
       16. The invention of claim 1 wherein: the wall strength of the pipe at the thread root adjacent the last engaged thread toward the smaller diameter end of the taper is substantially equal to the pipe wall strength at mid-section of the pipe so as to provide a connection strength greater than the pipe strength. 
     
     
       17. The invention of claim 2 wherein the thread depth is less than one-sixth of the pipe wall thickness. 
     
     
       18. A high efficiency connection for joints of oilwell tubing or the like, comprising: at least two pipes joined together and forming joints of pipe, each joints of pipe having a first end with no increase in wall thickness relative to the average pipe wall thickness and formed with tapered internal threads; the joints each having a second end formed with tapered external threads dimensioned such that one such joint may be sealingly connected directly with another such joint; the threads being of sufficient length and taper such that the pipe wall strength of the first end in the area of the smallest diameter of thread engagement is at least three-fourths of the average pipe wall strength of the joints of pipe. 
     
     
       19. The connection of claim 18 wherein: the second end is formed with a bore diameter through the external threads of smaller dimension than the average bore of the pipe.